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Kenya's interior minister says 9 people tied to mall attack are in custody

Authorities have interviewed 156 witnesses so far, he says

Lenku: There are no missing persons reports; Red Cross said 59 are missing

He calls a U.S. advisory on Kenya "uncalled for, unnecessary and unfriendly"

An additional suspect was arrested Sunday in connection with this month's terrorist attack at a mall in Kenya's capital, the country's interior minister said.

The arrest brings to nine the total number of people in police custody in connection with the attack on Nairobi's Westgate Shopping Mall, Interior Minister Joseph Ole Lenku told reporters.

He declined to release the identities or nationalities of the suspects allegedly involved in the September 21 terror attack, which resulted in a four-day standoff that left at least 67 people dead and parts of the shopping center destroyed.

"We believe it is premature and would jeopardize the results of the investigations if we go giving you the identities of the suspects arrested," Lenku said.

Lenku said authorities have interviewed 156 witnesses so far and found assault weapons in a vehicle they believe was used by terrorists involved in the attack.

But Lenku said Kenyan authorities have received no formal reports of missing persons, and believe that there were no hostages in the mall at the time the siege ended. The interior minister asked for aid agencies to forward any information they've received to the government.

"It is the government position that there were no hostages and we managed to rescue all people from the building," Lenku said.